1. Field of the Invention
The invention concerns a method for deboning fish, specifically fish of the mackerel and tuna family, by cutting out a slice of the fish containing the back spokes, the belly spokes and the vertebral column and cutting away slices of the fish containing the ribs. The invention also relates to an apparatus for carrying out such, method, the apparatus including a conveyor for advancing the fish in the direction of extension of their vertebral column, with the vertebral column being aligned with the plane of symmetry of the, fish, tool are arranged, respectively, on both sides of the conveying path for cutting out the back spokes, the belly spokes, the vertebral column and the ribs the tools for cutting out the ribs comprise, respectively, a knife having a point directed against the conveying direction of the fish and a cutting edge starting from the point and diverging with respect to the conveying path.
2. Prior Art
Fish of the tuna and mackerel family including mackerel (scomber scombrus, scomber japonicus) and tunny (thunnus thynnus) as such, but also types varying throughout different waters such as pelamid, bonito, sea bass and the like have a particular anatomical characteristic associated with the belly cavity, which is enclosed by ribs, namely the dorsal side of the cavity is not delimited by the vertebral column as is the case for fish of the gadus family but is spaced from the vertebral column over a substantial portion of the cavity length. Thus the fish of this family possess belly spokes in the region of the belly cavity, as well, which extend from the vertebral column towards the ribs enclosing the cavity. The belly spokes located in the region of the gill cavity are the shortest so that the dorsal side delimitation of the belly cavity against the vertebral column diverges towards the tail end of the fish. In other words, when viewed in cross-section of the fish, the belly spokes and the ribs together form a structure similar to an inverted Y, with the ribs forming the two arms and the foot being formed by the belly spokes. Towards the gills, the Y-shape increasingly changes to a V-shape as the belly spokes become progressively shorter and the ribs finally extend directly from the flanks of the vertebral column.
In a device for separating fillets from fish known from DE 29 46 942, the tool for cutting free the ribs consists of a scraping tool having scraping knives arranged on both sides of the fish conveying path with a counter support in the form of a support element. Each scraping knife has a cutting edge which starts at a point and diverges away from the conveying path in the conveying direction. The counter support is arranged adjacent the cutting edge to yield resiliently. After the belly and back spokes have been cut free at the tail-end of the fish! and the belly cavity and of the fish approaches the scraping knife, the point of the latter is guided into the trough formed between the back spokes and the start of the ribs on the vertebral column while the counter support supports the ribs from within the belly cavity. As the fish is advanced, the ribs are progressively separated from the fillet meat along their length.
The described function of the apparatus requires that the ribs remain connected to the fish bone structure throughout the separation operation so that the considerable clamping and separation forces applied to the ribs can be absorbed by the whole bone structure.
However, for the family of fish in question, the use of this known apparatus inevitably results in the ribs becoming detached from the bone structure when the belly spokes are being cut free. Consequently if bone-free fillets are required, the ribs must subsequently be cut away manually in a timeconsuming and costly manner.